Tackling a tough target: An ATP-sensitive channel

Injured and dying cells release lots of ATP, which triggers inflammation by binding to the ion channel P2X7. Interfering with this process could treat numerous diseases, but so far small-molecule drugs have not been potent or specific enough. Now, Danquah and colleagues have developed single-domain “mini antibodies” called nanobodies that rise to the challenge. One of their nanobodies blocked the P2X7 channel and inhibited disease in mouse models of kidney inflammation and contact dermatitis. Another nanobody dampened the release of inflammatory messengers from human cells 1000 times more effectively than the small-molecule drugs now under development. Nanobodies can be linked together to prolong their lifetime or confer cell specificity, a useful versatility that increases their appeal.

Abstract

Ion channels are desirable therapeutic targets, yet ion channel–directed drugs with high selectivity and few side effects are still needed. Unlike small-molecule inhibitors, antibodies are highly selective for target antigens but mostly fail to antagonize ion channel functions. Nanobodies—small, single-domain antibody fragments—may overcome these problems. P2X7 is a ligand-gated ion channel that, upon sensing adenosine 5′-triphosphate released by damaged cells, initiates a proinflammatory signaling cascade, including release of cytokines, such as interleukin-1β (IL-1β). To further explore its function, we generated and characterized nanobodies against mouse P2X7 that effectively blocked (13A7) or potentiated (14D5) gating of the channel. Systemic injection of nanobody 13A7 in mice blocked P2X7 on T cells and macrophages in vivo and ameliorated experimental glomerulonephritis and allergic contact dermatitis. We also generated nanobody Dano1, which specifically inhibited human P2X7. In endotoxin-treated human blood, Dano1 was 1000 times more potent in preventing IL-1β release than small-molecule P2X7 antagonists currently in clinical development. Our results show that nanobody technology can generate potent, specific therapeutics against ion channels, confirm P2X7 as a therapeutic target for inflammatory disorders, and characterize a potent new drug candidate that targets P2X7.